<template>
  <p>age: {{ age }}</p>
  <button @click="age++">update age</button>
</template>

<script>
import { isReactive, reactive, watch, ref } from 'vue'
export default {
  setup() {
    const age = ref(18)
    watch(age, (newValue, oldValue) => {
      console.log(newValue, oldValue)
    })
    return {
      age,
    }
  },
}
</script>
